It looks as no grading was used in karate before the belt system. As an Okinawan martial art karate didn’t use the Menkyo(license) grading of the traditional Japanese martial arts.
However with the Shimazu clan of satsuma in early 1600’s japanese martial arts was introduced on Okinawa and eventually some of the legendary karate masters gained mekyo ranks in those arts specifically Japanese sword art.
Further interesting, with judos introduction of Dan grades that karate adopted so did also the traditional Japanese sword school of satsuma, the one that some of the old karate master of Okinawa had gotten menkyo grades in.